Nitrocellulose solid propellant composition with load additive to reduce radar attenuation

ABSTRACT

1. A nitrocellulose propellant composition consisting essentially of an intimate admixture of about 10% to about 60% nitrocellulose, about 20% to about 50% energizing plasticizer for nitrocellulose, 0% to about 25% of a metallic fuel, about 1% to about 15% of a non-explosive plasticizer for nitrocellulose, about 1% to about 5% of a stabilizer, 0% to about 5% of a burning rate modifier, and from about 0.5% to about 5.0% of lead chromate, all percentages expressing percent by weight of total compositions.

United States Patent [191 Pierce Apr. 30, 1974 [75] Inventor:

[73] Assignee: The United States of America as represented by the Secretary of the Army, Washington, DC.

[22] Filed: May 22, 1964 [21] Appl. No.: 370,402

Everette M. Pierce, Somerville, Ala.

[52] US. Cl 149/18, 149/19, 149/20, 149/22, 149/35, 149/38, 149/39,

[51] Int. Cl C06d 5/06 [58] Field of Search 149/96, 97, 98, 99, 35, 149/38, 18, 19, 22, 20, 39

[56] References Cited UNITED STATES PATENTS 2,916,775 12/1959 O'Neill ..149/96 2/1961 Ryker 149/96 6/1964 Camp et al. 149/ Primary ExaminerBenjamin R. Padgett Attorney, Agent, or FirmEdward J. Kelly; Herbert Berl EXEMPLARY CLAIM 1. A nitrocellulose propellant composition consisting essentially of an intimate admixture of about 10% to about 60% nitrocellulose, about 20% to about 50% energizing plasticizer for nitrocellulose, 0% to about 25% of a metallic fuel, about 1% to about 15% of a non-explosive plasticizer for nitrocellulose, about 1% to about 5% of a stabilizer, 0% to about 5% of a burning rate modifier, and from about 0.5% to about 5.0% of lead chromate, all percentages expressing percent by weight of total compositions.

4 Claims, No Drawings NITROCELLULOSE SOLID PROPELLANT COMPOSITION WITH LOAD ADDITIVE TO REDUCE RADAR ATTENUATION The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

The present invention relates to a method for decreasing the radar attenuation caused by the exhaust gases from a solid propellant rocket motor and to improved propellant compositions. Particularly, the invention relates to a method for decreasing the amount of radar attenuation due to the combustion of nitrocellulose base propellant formulations and especially double-base propellant formulations by incorporating powdered lead chromate therein. Novel nitrocellulose base compositions containing lead chromate are also contemplated by the invention.

The guidance of many missile systems depends on the effective transmission and receiving of ultra highfrequency waves. It has been found that the hot exhaust gases from these solid propellants attenuate the radar signal used in the guidance of the missile. For example, potassium and sodium salts present in the propellant as impurities cause attenuation of the radar signal. Furthermore, during combustion those propellants which utilize particulate metal as high energy fuel additives seriously weaken the radar signal. Therefore, a means of eliminating or substantially reducing the amount of attenuation is needed to improve the accuracy of the particular missile involved.

It has now been determined that a small amount of lead chromate incorporated into nitrocellulose-base propellant compositions greatly reduces the attenuating effect of the exhaust gases. Moreover, the lead chromate even reduces the attenuating effect in those compositions which contain high energy metallic fuels.

In accordance with the foregoing, it is an object of the present invention to provide improved nitrocellulose base solid propellant compositions containing lead chromate, these compositions having greatly reduced radar attenuating effects.

A further object is to provide a method for reducing the radar attenuating effects of double-base propellants by incorporating lead chromate into the propellant compositions.

The manner in which these as well as other objects can be accomplished will become apparent from the following detailed description.

The terminology nitrocellulose-base solid propellant composition is intended to include any propellant composition based on a colloid of nitrocellulose and a plasticizer for the nitrocellulose. The plasticizer can be either the explosive or energizing type, the nonexplosive type, or a combination of the two. It is to be understood that while the invention is discussed in detail with relationship to double-base compositions, the invention is equally applicable to any nitrocellulose base composition. Therefore, by substituting one or more conventional plasticizers for nitrocellulose for all or part of the nitroglycerin in the double-base compositions discussed hereafter, a wide range of suitable nitrocellulose-base propellants can be prepared.

Illustrative examples of the so-called energizing plasticizer include but are not limited to the nitrate esters of polyhydric alcohols such as nitroglycerin, butanetriol trinitrate, and diethyleneglycol dinitrate.

As used herein, the term double-base composition is intended to include those compositions based on a colloid of nitrocellulose and nitroglycerin; that is, compositions containing at least 40% by weight of the colloid. Such propellants are well known in the art with detailed examples being available in US. Pat. Nos. 2,967,098; 2,982,638; 3,093,523; 3,102,834; 3,103,458; 3,104,190. In its basic form, the invention contemplates compositions consisting essentially of about to about 99.5% of the nitrocellulose-nitroglycerin colloid and about 0.5% to about 5.0% powered lead chromate. However, the compositions can and normally will contain various amounts of stabilizers, modifier, additional plasticizers, and the like. Preferably, the compositions will consist essentially of an intimate admixture of the following components in about the specified percentage ranges:

The nitrocellulose will contain at least 12.5% nitrogen and may contain up to 13.5% nitrogen. Moreover, the nitrocellulose can be used in the form of ball powder. As metallic fuels, there can be used aluminum, boron, magnesium, alloys of these metals with each other, aluminum hydride, borohydrides, and the like. Generally, the metallic fuel will not exceed about 10% by weight of the composition. Of the metallic fuels, aluminum is the most preferred.

There are many art-recognized non-explosive plasticizers for nitrocellulose which are suitable for use in the invention. Among these are the following: organic phosphate esters such as tributoxyethyl phosphate and octyldiphenyl phosphate; phthalate esters such as dioctyl phthalate, dimenthyl phthalate, and dibutyl phthalate; the diesters of adipic. acid, succinic acid, and sebacic acid as exemplified by dibutyl succinate, dibutyl adipate, dioctyl sebacate dioctyl adipate, and dibutyl sebacate; triacetin; triethylene glycol, orthonitrobiphenyl, and di-2-ethyl butyrate.

The stabilizer can be one or more of the following compounds: 2-nitrodiphenylamine, symmetrical diethyl diphenyl urea, diphenylamine, methylethyldiphenyl urea, resoricinol, and the like. The preferred stabilizer system is based on the use of resorcinol and 2- nitrodiphenylamine in combination.

At least one burning rate modifier may be incorporated into the compositions such as lead salicylate, lead acetylsalicylate, lead azide, lead stearate, lead oxide, ammonium perchlorate, various dyes, and the like. The compositions can also contain carbon black, candelia wax, and inert fillers.

According to the present invention, the radar attenuation of double-base propellant compositions of the type discussed hereinabove is reduced at least 20% by incorporating into the composition about 0.5% to 5.0% by weight of powdered lead chromate. In most instances, the amount of reduction is considerably higher and in some cases can approach 90%. This reduction in radar attenuation makes it possible to utilize the highly perfected double-base propellants in radarcontrolled missiles, particularly antimissile systems requiring the utmost in accuracy. As previously stated, the actual reduction in the amount of attenuation will depend on the amount of lead chromate used and the particular double-base propellant composition.

The improved compositions of the invention are prepared according to two well known standard techniques. For example, using a water-jacketed Sigma blade mixer to insure uniform distribution of all ingredients, extruded grains can be made in the following manner. The nitrocellulose is wet with ethanol and the nitroglycerin desensitized with acetone. Thereafter, the nitroglycerin, nitrocellulose, metallic fuel, nonexplosive plasticizer, stabilizer, modifiers, and lead chromate are blended in the mixer. Additional acetone is added to the mixture to achieve a ratio of solvent to dry nitrocellulose of about 08:10. All the ingredients are mixed for several hours then partially dried. Subsequently, the mix is extruded into grains of the desired size by means of a hydraulic press. After a drying period of about 3 to days, the grains are cured (colloided) and substantially solvent free. Using this procedure, propellants having the following compositions are readily prepared.

enter the exhaust stream with a valence of six. Free electrons in the exhaust stream (which are at least responsible for some of the attenuation) are picked up by the chromium ions. If there are enough free electrons in the exhaust gases, the chromium ions probably collect up to three electrons with a corresponding valence change to three. For this reason, it is very possible that other chromate salts can accomplish a similar reduction in the amount of radar attenuation.

The above detailed description is for purposes of illustration only and no undue limitation should be ascribed to the invention as a result thereof except as reflected in the appended claims.

1 claim:

1. A nitrocellulose propellant composition consisting essentially of an intimate admixture of about 10% to about 60% nitrocellulose, about 20% to about energizing plasticizer for nitrocellulose, 0% to about 25% of a metallic fuel, about 1% to about 15% of a nonexplosive plasticizer for nitrocellulose, about 1% to about 5% of a stabilizer, 0% to about 5% of a burning rate modifier, and from about 0.5% to about 5.0% of lead chromate, all percentages expressing percent by weight of total compositions.

2. A double-base propellant composition consisting essentially of an intimate admixture of about 10% to about 60% nitrocellulose with said nitrocellulose containing about 12.5% to about 13.5% by weight nitro- Weight Percent of Ingredient in Composition 11 Ill Nitrogen content of nitrocellulose: l-l2.6%N; 1I-13.1%N; Ill-12.5%N

Using conventional mixing equipment, the Slurry" or Plastisol type propellants are prepared using ball powder as the source for nitrocellulose. All the ingredients are mixed at ambient temperature for 10 to 60 minutes, poured into molds or motors, and cured at elevated temperatures. Typical Slurry cast propellant compositions are as follows:

Z-Nitrodyphenylamine 2% The exact mechanism by which the lead chromatc decreases the amount of radar attenuation is not understood. However, it is believed that the chromium ions gen, about 20% to about 50% nitroglycerin, 0% to about 25% of a metallic fuel selected from the group consisting of aluminum, boron, magnesium, alloys of these metals with each other, aluminum hydride, and borohydrides, about 1% to about 15% of a nonexplosive plasticizer for said nitrocellulose selected from the group consisting of organic phosphate esters, phthalate esters, diesters of adipic acid, diesters of succinic acid, diesters of sebacic acid, triacetin, triethylene glycol, orthonitrobiphenyl, and di-Z-ethyl butyrate, about 1% to about 5% of at least one stabilizer selected from the group consisting of 2-nitrodiphenylamine, symmetrical diethyl diphenyl urea, resorcinol, diphenylamine, and methylethyldiphenyl urea, 0% to about 5% of at least one burning rate modifier selected from the group consisting of lead salicylate, lead acetylsalicylate, lead azide, lead stearate, lead oxide, ethyl centralite, cellulose acetate, ammonium nitrate, and ammonium perchlorate, and about 0.5% to about 5.0% lead chromate, all percentages expressing percent by weight of total composition.

6 4. The method according to claim 3 wherein said lead chromate is present in an amount equal to about 0.5% to about 5.0% by weight of the total weight of said composition including the weight of said lead chromate. 

1. A NITROCELLULOSE PROPELLANT COMPOSITION CONSISTING ESSENTIALLY OF AN INTIMATE ADMIXTURE OF ABOUT 10% TO ABOUT 60% NITROCELLULOSE, 0% TO ABOUT 25% OF A METALLIC PLASTICIZER FOR NITROCELLULOSE, 0% TO ABOUT 25% OF METALLIC FUEL, ABOUT 1% TO ABOUT 15% OF A NON-EXPOLSIVE PLASTICIZER FOR INTROCELULOSE, ABOUT 1% TO ABOUT 5% OF A STABILIZER, 0% TO ABOUT 5% OF A BURNING RATE MODIFIER, AND FROM ABOUT 0.5% TO ABOUT 50.% OF LEAD CHROMATE, ALL PERCENTAGES EXPRESSING PERCENT BY WEIGHT OF TOTAL COMPOSITIONS.
 2. A double-base propellant composition consisting essentially of an intimate admixture of about 10% to about 60% nitrocellulose with said nitrocellulose containing about 12.5% to about 13.5% by weight nitrogen, about 20% to about 50% nitroglycerin, 0% to about 25% of a metallic fuel selected from the group consisting of aluminum, boron, magnesium, alloys of these metals with each other, aluminum hydride, and borohydrides, about 1% to about 15% of a non-explosive plasticizer for said nitrocellulose selected from the group consisting of organic phosphate esters, phthalate esters, diesters of adipic acid, diesters of succinic acid, diesters of sebacic acid, triacetin, triethylene glycol, orthonitrobiphenyl, and di-2-ethyl butyrate, about 1% to about 5% of at least one stabilizer selected from the group consisting of 2-nitrodiphenylamine, symmetrical diethyl diphenyl urea, resorcinol, diphenylamine, and methylethyldiphenyl urea, 0% to about 5% of at least one burning rate modifier selected from the group consisting of lead salicylate, lead acetylsalicylate, lead azide, lead stearate, lead oxide, ethyl centralite, cellulose acetate, ammonium nitrate, and ammonium perchlorate, and about 0.5% to about 5.0% lead chromate, all percentages expressing percent by weight of total composition.
 3. In rocket motors, the method for decreasing the amount of radar attenuation due to the exhaust gases for burning, double-base, solid propellant compositions, said method comprising incorporating into said composition and uniformly dispersing therethrough before combustion powdered lead chromate.
 4. The method according to claim 3 wherein said lead chromate is present in an amount equal to about 0.5% to about 5.0% by weight of the total weight of said composition including the weight of said lead chromate. 